In a manufacturing process of semiconductor devices, a plasma etching process or the like is performed. With the miniaturization of electronic devices, it is required to form fine patterns with high precision in the plasma etching process. By way of example, it is required to form a deep hole in an etching target layer with high precision.
As one kind of semiconductor devices manufactured by the plasma etching process of forming a deep hole, there is known a NAND type flash memory device having a three-dimensional structure. In the manufacture of the three-dimensional NAND type flash memory device, there is performed a process of etching a multilayered film, in which two kinds of layers having different relative permittivities are alternately stacked on top of each other, so that a deep hole is formed in the multilayered film.
As the plasma etching of forming such a deep hole, there is known a plasma etching method as described in Patent Document 1. In the plasma etching of Patent Document 1, a cycle including a first process of setting a flow rate of at least one kind of gas, among plural kinds of gases, to be a first flow rate during a first period; and a second process of setting a flow rate of the corresponding one kind of gas to be a second flow rate different from the first flow rate during a second period is repeated under the presence of plasma.
Patent Document 1: Japanese Patent Laid-open Publication No. 2011-165769
In the plasma etching method described in Patent Document 1, since a reaction product is deposited on a surface of a mask, it is possible to etch an etching target layer with a high selectivity against the mask. This method, however, also has problems. That is, if the reaction product is deposited on the surface of the mask in a non-uniform manner, an extending direction of a hole formed in the etching target layer may be changed as the etching process proceeds. In the following description, a phenomenon that an extending direction of a space such as a hole formed in the etching target layer is changed as the etching process proceeds, that is, a phenomenon that an extending direction of the space is changed from a certain position of the etching target layer in a thickness direction thereof may be referred to as “direction change of space.”
In view of the foregoing, it is required to suppress the direction change of space formed in the etching target layer while maintaining the etching selectivity for the etching target layer against the mask.